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  • TI Thinks Resolved

LMZ14201H: GND (pin #4) and Exposed Pad Connection

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Part Number: LMZ14201H

Hello,

I am using the LMZ1420XH series in many projects as a preliminary DC-DC converter for the first stage of the circuit, continued in the second stage by linear LED drivers.

Recently some EMI tests failed at unexpected high frequencies with peaks at 60MHz, 150MHz and 300MHz.

The module's frequency is set below 300KHz .

We consulted with several engineers and some recommended to remove the PCB track that connects the EP to the GND pin.

Although according to the LMZ data sheet the GND pin should be externally connected to the EP, they claim that noise or oscillation might be induced if connected.

Is this correct? Is the GND pin internally connected to the EP?

What is your recommendation?

Thanks

 

  • Hi Emanuel,

    EP and pin 4 (GND) are internally connected. However, it it still recommended to physically connect them for thermal purposes. 

    Figure 49 in the datasheet shows the two critical current loops that can affect EMI. Perhaps a recommendation to reduce EMI noise is by placing the input capacitors closer to the VIN(pin1). Also make sure that the feedback resistors are close to FB(pin6) and make the trace length and size small.

    Regards,

    Jimmy 

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